JPS6012553B2 - Tunnel furnace control method for reduction firing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling a tunnel furnace in which a reduction zone maintained in a reducing atmosphere is provided in a part of the firing zone formed in the longitudinal center of a tunnel-shaped furnace body.

The tunnel furnace that performs reduction firing is as shown in Figure 1.
A firing zone B is constructed in which a large number of burners 4 are arranged in a row at the center of a tunnel-shaped furnace body 1 in the longitudinal direction, which has an inlet 2 for carrying in the materials to be fired at one end and an outlet 3 at the other end. , by penetrating the suction pipe 6 of the blower 5 installed near the carry-in port 2 into the furnace body 1, and by penetrating the discharge pipe 8 of the blower 7 installed near the carry-out port 3 into the furnace body 1, By driving both blowers 5 and 7, a pressure gradient is formed where the pressure gradient is high on the carry-out port 3 side and low at the carry-in port 2, and an airflow is generated in the furnace body 1 from the carry-in port 3 side toward the carry-in port 2 side, and the firing zone B On the carry-in port 2 side of the firing zone B, there is a preheating zone A that uses high-temperature gas flowing in from the firing zone B to pre-heat the materials to be fired immediately after being carried in, and on the carry-in port 3 side of the firing zone B Cooling zones C are formed in which the objects to be fired heated to the maximum temperature are cooled by air blown in from outside the furnace, and in the firing zone B, from the carry-out port 3 side toward the carry-in port 2 side, Neutral band B1 maintained in a neutral atmosphere,
The reduction zone B2 is maintained in a reducing atmosphere, and outside air is blown into the furnace body 1 by the blower 9 that penetrates the discharge pipe 10 to create the reduction zone B2.
The atmosphere in each zone is determined by the air/fuel ratio of each burner, and the atmosphere in each zone is determined by the air/fuel ratio of each burner. Neutral band BI is kept at the highest temperature. Then, the temperature inside the furnace is detected for each zone, and if it deviates from the standard temperature, the fuel supplied to the burner 4 is increased or decreased to return it to the standard temperature, and the amount of air supplied is increased or decreased in proportion to the fuel. Automatic control is performed to keep the ambient temperature constant, but the airflow inside the furnace body 1 from the carry-out port 3 side to the carry-in port 2 side is caused by the upper surface of the object to be fired and the ceiling surface of the furnace body 1. While it flows vigorously through the space constructed between
Since the lower part of the furnace body is difficult to flow because it is obstructed by the trolley etc. of the materials to be fired, in the reduction zone B2, the upper part of the furnace body 1 where there is a large amount of inflow of hot air from the neutral zone BI, and the burner 4 are There is a large difference in reducing atmosphere concentration between the lower part of the furnace body 1 and the lower part of the furnace body 1, and it is not possible to maintain the atmosphere concentration in the upper and lower parts of the furnace body 1 at the standard value by simply controlling the air-fuel ratio of the burner 4. It is difficult.

In the present invention, the atmosphere near the burner is controlled by the air-fuel ratio of the burner, and the atmosphere in the upper part of the furnace body is controlled by the flow rate of the airflow flowing from the delivery port toward the delivery port. The purpose is to uniformly control the temperature, and one embodiment thereof will be explained based on the attached drawings. Atmosphere detection tubes 22 provided in spaces b and c formed between the ceiling surfaces of the body 1,
The CO gas concentration of the furnace gas taken out by step 11 is C
Detected by the O analyzers 23 and 12, the detected values are input as electrical signals to the calculation devices 24 and 15, and the output signal of one calculation device 24 based on the result of calculation based on the input signal is used to generate the output signal shown in FIG. As shown, the opening degree of the bleed valve 26 is adjusted to control the secondary side pressure of the pressure regulating valve 25, and the ratio of fuel and air supplied to the burner 4 in the reduction zone B2 is changed, mainly to the furnace body. The atmosphere in the lower space b is controlled to maintain a predetermined CO concentration, but the other computing device 1
The output signal of 5 is input to the rotation speed control devices 20 and 21,
Depending on the output, Proa 7 or cooling zone C firing zone B
The rotational speed of the blower 18 installed closer to the furnace body 1 through the suction pipe 19 is changed, and the flow rate of air flowing from the cooling zone C to the firing zone B is changed. When the CO analyzer 12 detects that the CO gas concentration in the upper space c in B2 has become higher than the standard value, the furnace body 1
Either the rotational speed of the blower 7 on the side of the outlet 3 that blows air into the furnace increases, or the rotational speed of the blower 18 that discharges gas from the furnace to the outside of the furnace decreases and the gas flows from the cooling zone C to the firing zone B. As the amount of air increases, excess CO in reduction zone B2
When the gas is combusted and its concentration is lowered, and conversely the CO gas concentration is lowered, the number of revolutions of the discharge blower 18 increases or not.

The rotational speed of A7 decreases, the amount of air flowing from the cooling zone C to the firing zone B decreases, the lack of oxygen in the reduction zone B2 is promoted, and control is performed in the direction of increasing the CO gas concentration. It is. In this embodiment, the 02 concentration detection tubes 13 and the pressure detection tubes 16 are inserted into the neutral zone BI of the furnace body 1, and the detected values are detected by the 02 analyzer 14.
is connected to the transmitter 17' so that it is converted into an electrical signal and inputted to the arithmetic unit 15, and the C in the reduction zone B2 is
Prior to the above control based on fluctuations in O concentration, neutral zone B
Blower 7 based on fluctuations in furnace pressure and 02 concentration in I
, 18.

This was done in order to eliminate the delay time that occurs when the reduction zone B2 is affected by changes in the rotational speed of the blowers 7 and 18 since the reduction zone B2 is separated from the cooling zone C. Therefore, the 02 concentration in the upstream neutral zone BI immediately affects the CO concentration in the downstream reduction zone B2,
Furthermore, since the furnace pressure in the neutral zone BI determines the flow rate of the airflow flowing into the downstream reduction zone B2, the cooling zone C
By detecting fluctuations in furnace pressure and 02 concentration in the neutral zone BI adjacent to the BI and controlling the rotational speed of the blowers 7 and 18 in advance, the response speed of automatic control of the CO concentration in the reduction zone B2 is increased and more strict control is achieved. This system is designed to perform accurate furnace pressure control.

As specifically explained in the above embodiments, the method for controlling a tunnel furnace of the present invention includes arranging burners in a row in the central part of the tunnel-shaped furnace body in the longitudinal direction to form a firing zone, and By maintaining the air pressure inside the furnace so that the loading port side is higher than the loading port side and generating an airflow from the loading port side to the loading port side, a child tropical zone is placed on the loading port side of the firing zone, and a subtropical zone is placed on the loading port side of the firing zone. In addition to configuring each cooling zone, the inside of the firing zone is sequentially divided from the carry-out port side to the carry-in port side: a neutral zone kept in a neutral atmosphere, a reduction zone kept in a reducing atmosphere, and air introduced into the furnace. In a tunnel furnace that is divided into a purification zone where the reducing gas flowing in from the reduction zone is completely combusted and an oxidation zone where an oxidizing atmosphere is maintained, the inside of the furnace body is separated from the exit side based on the change in the reducing atmosphere concentration in the reduction zone. The purpose is to control the flow rate of the airflow toward the loading port side, and maintain the reducing atmosphere concentration in the upper part of the furnace body at a desired value, which is difficult to control only by adjusting the air-fuel ratio using the burner. This has the effect of maintaining uniform firing conditions in the upper and lower parts of the furnace body.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a tunnel furnace used to carry out the method of the present invention, together with a block diagram of the control circuit.
The figure shows a cross-sectional view of the furnace body in the reduction zone along with a block diagram of the control circuit. 1: Furnace body, 2: Loading port, 3: Loading port, 4: Burner, 5,
7, 9, 18: Blower, 11, 22: CO concentration detection tube,
13:02 Concentration detection tube, 16: Pressure detection tube, 12, 23
:CO concentration analyzer, 14:02 concentration analyzer, 17: Transmitter, 15, 24: Arithmetic device, 20, 21: Control device, 2
5: Pressure adjustment valve, 26: Bleed valve, A: Pre-preparation zone, B:
Calcining zone, C: Cooling zone, BI: Neutral zone, B2: Reduction zone, B
3: Purification zone, B4: Oxidation zone. Technique 1 Nezushige 2

Claims (1)

[Claims] 1. Burners are arranged in a row in the longitudinal center of a tunnel-shaped furnace body to form a firing zone, and the pressure inside the furnace body is made higher on the outlet side than on the entrance side. By maintaining the air flow from the carrying-out port side to the carrying-in port side, a preheating zone is formed on the carrying-in port side of the firing zone, and a cooling zone is formed on the carrying-out port side. From the outlet side to the entrance side, the neutral zone kept in a neutral atmosphere, the reduction zone kept in a reducing atmosphere, and purification by blowing air into the furnace to completely burn the reducing gas flowing from the reduction zone. The tunnel furnace is divided into an oxidizing zone and an oxidizing zone maintained in an oxidizing atmosphere, and is characterized in that the flow rate of the air flow from the carrying-out port side to the carrying-in port side in the furnace body is controlled based on changes in the reducing atmosphere concentration in the reducing zone. A method for controlling a tunnel furnace. 2. The method for controlling a tunnel furnace according to claim 1, characterized in that the flow rate of the airflow is controlled in advance based on fluctuations in the pressure inside the furnace. 3. The tunnel furnace control method according to claim 1, further comprising controlling the flow rate of the air flow in advance based on a change in the oxidizing atmosphere concentration in the neutral zone.